Excellent question on the stregth of the fasteners Brian. I should have included this in the introduction, so here are the specs per fastener. There are two sizes, regular for the smaller cases (1500 series thru 3200 series) and heavy duty for the larger cases (5500 & 7300 series):
Specifications Per Single Fastener: Regular - Heavy Duty
Max. Working Tensile Strength: 120lbs (530 N) - 560lbs (2400 N)
Average Ultimate Strength 500lbs (2220 N) - 1000lbs (4450 N)
Max. Working Shear Strength 700lbs (3110 N) - 1250lbs (5560 N)
Receptacle Pull-Out Force T-6 Aluminum Base 336lbs (1494 N) - 336lbs (1494 N)
Testing was done with my Toyota T-100 4x4 truck with stiff suspension. We loaded one 60lb bag of concrete in the smaller cases, and two bags (120lb) in the larger cases. Terrain included washboards, deep ruts, rocks, slow and high speed. We also mounted a 2100 series case vertically and ran the same tests. Then we mounted the larger cases on a Yakima rack and did the same tests. No failures and no problems (except for bent tubing and deformed truck bed rails). Then we intentionally weakened the QFS bases to create an easier pull-out force on the fastener receptacle and still no problems. Since this product is very customizeable to each user's requirements you may certainly add more fasteners to the larger cases if you see the need. There are those among us that can break an anvil (you know who you are), and as with our motorcycle luggage products we'll always strive to make the product more crash proof based on field data. Please take a close look at the downloadable documents on our web site here
http://cariboucargo.com/?name=Downloads to see some of the things we've done in design to make this system strong.
With regard to racks, I spoke at length with the folks from several manufacturers. With our rail kits included it is very straight forward whether the rack basket has a tubular floor or flat plate (our rails are readily available 1" x 1/2" x 1/8" steel channel). If you don't use the rail kits, it is still straightforward for the flat plate floor type, but the tubular type gets a bit more tricky due to spacing. The lowest profile of the fastener base, not using rails, is 1/8". With rails it is 5/8" high for the regular and 7/8" high for the heavy duty. I hope to eventually have some photos of installs on racks.
Thank you, good questions.